1. Invention
This invention relates generally to conveyer systems and more particularly to roller-ball transfer systems including ball transfer mats with inserted ball transfer units.
2. Description of the Prior Art
Referring to FIG. 1A, ball transfer units (BTUs) 100 are used as part of a system to move cargo and material along a surface. A ball transfer unit (BTU) 100 is round and cylindrical in shape having a main ball bearing that supports various loads and provides for movement of a load along a surface. BTUs have generally been installed into a ball transfer mat 101 that is placed upon the surface the load was to move over. A ball transfer mat 101 is generally made of a thick steel decking. A symmetry of holes 103A are drilled into the decking wherever a BTU may be expected to be inserted. The BTUs 100 are typically positioned into predetermined holes such as 103A in the upper surface of the ball transfer mat 101.
Typically, a series of ball transfer mats 101 are symmetrically placed in a warehouse, air cargo bin, truck bed, or other material handling facility. The series of ball transfer mats may be used to move a variety of loads in settings such as air, truck, or maritime cargo forwarding facilities; warehouses; factories; and military bases, munition depots and supply bases. Ball transfer mats 101 having BTUs reduces the requirement of movement of a load by forklift, caster strips or other means that are more likely to damage a cargo container or the cargo itself. A system of ball transfer mats having BTUs also enables cargo to be moved more quickly and efficiently than other methods and reduces the risk of occupational injuries which may occur when forklifts, caster strips or human beings carry a load.
Referring to BTU 100 in FIG. 1B, a ball transfer unit essentially includes a round cylindrical housing 120 with an open mouth that serves as an enclosure for the entire unit, a cup-shaped race 122 that sits snugly inside the housing 120, a number of small diameter ball bearings 124 that sit in the race 122, a main ball bearing 126, and a cap 128 that encompasses the mouth of the housing and snaps into place holding the interior contents 122, 124 and 126 to the housing 120 while still allowing all the ball bearings 126 and 124 to roll freely. The main ball bearing 126 within a BTU is capable of rolling in any direction so that loads such as parcels or air cargo bins may be moved along a surface in any direction when a force is applied.
To perform properly, the main ball bearing 126 in the BTU 100 needs to roll freely in each direction such that loads may be easily pushed along the ball transfer mat. Furthermore, the BTUs 100 need to function indoors as well as outdoors since material handling facilities may exist in either environment. Each BTU within a ball transfer mat may support a load that is relatively light--less than twenty-five pounds--such as a box of semiconductor chips or it may support a full air cargo container weighing more than fifteen-thousand pounds. It is desirable that BTUs be made of noncorrosive materials that are able to withstand anticipated climate and environmental corrosive elements, such as rain, mud, dirt, dust, heat, snow, freezing temperatures, salt and anti-freeze chemicals that may be applied to streets or airport runways during snow storms. It also desirable that a BTU be manufactured using materials that can withstand the weight of anticipated loads.
Previously, all components 120-128 of the BTUs were manufactured out of metal such as steel or aluminum. The material handling industry believed that metal components were necessary in order for a BTU to have the structural strength needed to handle heavy loads. These metal components of the BTUs are often plated with zinc or another similar material in order to resist corrosion. While this plating process adds to the cost and labor needed to manufacture a BTU it does somewhat protect a metal BTU and extend its useful life. However, the plating process involves the use of some toxic chemicals that should be carefully handled.
In order to reduce the cost of a BTU, the material used to manufacture the cap 128 of the BTU was changed from a plated metal to a plastic. It was understood that the plastic would be sufficient to keep the BTU 100 assembly together.
Referring to FIG. 1B, the shape of the housing 120 is cylindrical. This shape has persisted in the material handling industries because BTU mats 101 are fitted with round holes of a fixed dimension. Furthermore the holes 103A are located in predetermined positions based upon the loads that are expected to be supported. The cylindrical shape of the BTU and its metal construction has limited the effective use of BTUs. Also, purchasing ball transfer mats having a number of BTUs is very costly. Also, moving cargo with hand trucks or forklifts may be less efficient. Purchasing costs are of a particularly concern to small businesses, medium businesses, government facilities with small budgets, third world and developing countries. It is desirable to reduce the purchase costs of a system of BTUs by retrofitting existing facilities.
Attempts have been made to adapt or retrofit the prior art BTU 100 to other settings but these attempts have proven costly, inefficient, and have sometimes damaged equipment. For example, consider a material handling facility that currently has no ball transfer mats that could contain BTUs and which presently uses hand trucks or forklifts. Often where hand trucks and forklifts are used, a grating system on the floor of the material handling facility is present. The grating system typically includes a series of metal grates. Each metal grate may be comprised of a number of individual polygonal shaped openings such as the square openings or holes 104 illustrated by the grating 102 in FIG. 1C. These openings or holes 104 are generally not large enough to accommodate the circular shaped or cylindrical BTU 100. The lower outer portion of the cylindrical housing 120 for the BTU is approximately one and eight-tenths inches in diameter. The typical square grating such as illustrated by FIG. 1C is a two inch by two inch square having a square opening or hole 104 that measures one and three-fourths inches by one and three-fourths inches. Thus, the diameter of the cylindrical housing 120 of the prior art BTU 100 exceeds the hole dimension 104. The individual bar thickness is typically one-fourth of an inch while the depth of the grating is typically one to two inches. It is desirable to insert a BTU into such a grating in a symmetric fashion every eight to ten inches from center to center. Sometimes it is desirable to place two BTUs next to one another in order to share the load at that point. In order to insert or retrofit the standard circular shaped or cylindrical BTU 100, the square holes 104 are first crudely expanded or wallowed out with a tool such as a pry bar. If the resultant circular hole 103B is too large, the BTU 100 may work its way out of the hole 103B. If the resultant circular hole 103B is too small, the BTU 100 may be squeezed and cause failure or a reduced life span in the BTU 100. Expanding the hole in size to the circular hole 103B generally prohibits the placing of another BTU beside the BTU 100 because the holes surrounding 103B have been reduced in size.
The use of the prior art BTU 100 in retrofitting a grating system causes a number of other problems. First, it is time consuming for workers to widen each hole 103B. Second, widening of a hole such as 104 distorts the grating itself and threatens the structural integrity of the grating and the carrying capacity of large loads. Third, because the widening of each opening is crudely performed, it is not uniform and thus is inherently incompatible with the circular shaped or cylindrical BTU. Furthermore, the BTU's housing and internal race can often get distorted by an imperfect fit. Fourth, the structural nature of the metal BTU does not afford an even distribution of weight to the sides of the grating hole 103B, resulting in uneven stress and distortion to the grating and the BTU. Lastly, the removal of a failed BTU from the grating at the end of its useful life or upon malfunction requires additional tool-work which may further damage the grating and the failed BTU. Also, where metal BTUs are retrofitted into a metal grating, it has been discovered that the movement of cargo creates a high volume of noise. As a result, workers in such facilities must wear hearing protection in order to avoid the risk of injuring their hearing.
Another problem associated with the prior art BTU 100 is that it has a limited useful life. Typically a metal BTU may have a useful life between six and twenty four months. At the end of a BTU's life, one can either dispose of it or have it rebuilt. If BTUs are to be disposed, one must arrange to have failed BTUs removed, gathered up, and disposed of in a waste landfill or other appropriate disposal cite. In order to rebuild BTUs, the failed BTUs are ordinarily shipped to a rebuilder. Usually a user waits until a sufficient number of BTUs have failed before sending them off to be rebuilt. Thus the user must often wait and store failed BTUs and purchase new BTUs in the mean time. It is desirable to exceed the mean time between failures of prior art BTUs.
In the case that BTUs are to be disposed of none of the material within the components are recycled which imposes a burden on landfills. If the BTUs are rebuilt, some of the components will be reused but others are defective and are replaced with new counterparts. Defective components are generally not recycled because of the difficulty and cost of doing so. It is desirable to make more of the components recyclable.